X-ray mammography is the standard of care for breast cancer screening, diagnosis, and stereotactic image-guided intervention. However, it is ineffective in women with radiographically dense breast tissue, who comprise about half of women over age 40. Recently, “3D mammography” (“tomosynthesis”) was introduced to partially alleviate the challenge of dense breast tissue. It enables a small improvement over planar mammography (digital or film), but it still suffers from the fact that cancer and dense tissue look similar on x-ray transmission images. Dense breast tissue is transparent to gamma photon emission, making MBI a potentially superior solution. Several commercial solutions have been offered. Naviscan introduced a PET solution labeled PEM (positron emission mammography), but the cost and dose are too high, reimbursement is a challenge, and a significant fraction of tumors cannot be detected with 18F-FDG. Three companies have introduced single-photon emission MBI products: Dilon Technologies offers a single scintillator camera solution at lowest cost but highest dose; Gamma Medica and General Electric both offer dual CZT (CdZnTe solid-state direct conversion) camera solutions. The cost of the CZT cameras is still high, although the effective dose has been reduced by to be nearly equivalent to screening mammography. Reimbursement for single-photon MBI is better than PET, but it is still challenging. Neither Gamma Medica nor General Electric yet offer a biopsy-guidance solution, which has hindered adoption.
Expired U.S. Pat. No. 5,519,221 (Weinberg, Naviscan) describes a generic MBI apparatus and method (FIG. 1) in which the breast is lightly compressed (painlessly immobilized) by two compression plates (also known as “paddles”). Two gamma cameras, offset by some distance, record multiple image views to be reconstructed into a tomosynthetic image. One of the most significant drawbacks of this design is poor image resolution because of the long distance from the collimator to the breast tissue. U.S. Pat. No. 6,377,838 (Iwanczyk and Patt, Gamma Medica) describes an MBI apparatus and method (FIG. 2) in which the compression paddles are eliminated and the collimators of the two gamma cameras are in direct contact with the breast tissue and thus form an integral part of the compression mechanism. This patent also requires the retrofitted attachment of the MBI gamma cameras to a mammography machine.
U.S. Pat. Nos 8,217,357 and 8,592,772 (Stein, et al., Hologic) describe an integrated x-ray tomosynthesis and MBI system with sequential imaging by the two modalities. The use of slanted parallel-hole collimators for stereotactic imaging of lesions for biopsy guidance is described as well as several schemes for moving one of a pair of gamma cameras to create access for a biopsy needle. U.S. Pat. Nos. 8,115,171 and 8,541,748 (Blevis, General Electric) describe MBI biopsy guidance using two gamma cameras positioned at an angle (typically 90 degrees) to each other to provide stereotactic imaging of lesions for biopsy guidance. U.S. Pat. No. 8,610,076 (Blevis, General Electric) describes a generic MBI system with pixelated CZT gamma cameras and pixel-registered collimators.
U.S. Pat. Nos 8,886,293 and 9,060,732 (O'Connor, Mayo Foundation) describe a highly focused collimator for real-time biopsy guidance. While the concept is sound, the embodiment is very challenging and unlikely to be implemented in clinical practice. U.S. Pat. No. 8,853,635 and application 2016/0,007,944 (O'Connor, Mayo Foundation) describe a dual-modality ultrasound and MBI system where biopsy guidance is provided by ultrasound.